Liquid automatic dishwashing detergent compositions have recently received much attention, and the aqueous products have achieved commercial popularity.
The acceptance and popularity of the liquid formulations as compared to the more conventional powder product stems from the convenience and performance of the liquid products. However, even the best of the currently available liquid formulations still suffer form two major problems: product phase instability and bottle residue, and to some extent, cup leakage from the dispenser cup of the automatic dishwashing machine.
Representative patent art in this area includes Rek U.S. Pat. No. 4,556,504; Bush et al. U.S. Pat. No. 4,226,736; Ulrich U.S. Pat. No. 4,431,559; Sabatelli U.S. Pat. No. 4,147,650; Paucot U.S. Pat. No. 4,079,015; Leikhem U.S. Pat. No. 4,116,849; Milora U.S. Pat. No. 4,521,332; Jones U.S. Pat. No. 4,597,889; Heile U.S. Pat. No. 4,512,908; Laitem U.S. Pat. No. 4,753,748; Sabatelli U.S. Pat. No. 3,579,455; Hynam U.S. Pat. No. 3,684,722. Other patents relating to thickened aqueous detergent compositions include Ginn U.S. Pat. No. 3,060,124, U.S. Pat. No. 3,985,668; U.K. Patent Applications GB 2,116,199A and GB 240,450; U.S. Pat. No. 4,511,487; Drapier, et al. U.S. Pat. No. 4,752,409; U.S. Pat. No. Drapier, et al. 4,801,395; Ahmed et al. U.S. Pat. No. 4,889,653. Commonly assigned co-pending patents include, for example, Ser. No. 427,912 filed Oct. 24, 1989; Ser. No. 924,385, filed Oct. 29, 1986; Ser. No. 323,138, filed Mar. 13, 1989; Ser. No. 328,716, filed Mar. 27, 1989; Ser. No. 323,137, filed Mar. 13, 1989; Ser. No. 323,134, filed Mar. 13, 1989.
The solubilizing effect of potassium salts on sodium tripolyphosphate in aqueous detergent compositions is described in Smeets U.S. Pat. No. 3,720,621. This patent describes homogeneous liquid compositions containing 14 to 35 percent sodium tripolyphosphate, 0.1 to 50 percent of potassium and/or ammonium salt of an inorganic or organic acid, water, and optional surfactants, solubilizing agent, organic sequestering agent and other adjuvants.
Corring U.S. Pat. No. 4,836,948 discloses a viscoelastic gel detergent composition characterized by its viscosity under low and high shear conditions, pH, and steady state viscoelastic deformation compliance. The composition requires the presence of a polycarboxylate polymeric thickener, preferably a cross-linked polyacrylic acid. The compositions of this patent also, however, require a trivalent metal containing material, especially an aluminum containing material such as alumina. The compositions may further include a structuring chelant which may be a salt of carbonate, pyrophosphate or mixture thereof, and preferably the potassium salts.
The recently issued U.S. Pat. No. 4,859,358 discloses the incorporation of metal salts of long chain hydroxy fatty acids, as anti-tarnishing agents, which do not affect the viscosity of the compositions in thickened aqueous automatic dishwasher detergent compositions. The thickeners for these compositions may be a high molecular weight polycarboxylate polymer, such as those sold under the Carbopol trade name, and specific 600 and 900 series resins are mentioned. It is also disclosed that the compositions include entrained gas, e.g. air bubbles to further ensure stability. Amounts of air in the range of from about 1% to 20%, preferably from about 5 to 15% by volume, will lower the specific gravity of the overall composition to within from about 5% more than to about 10% less than, preferably from 1% more than to 5% less than, the specific gravity of the aqueous phase. In Example III of this patent, the specific gravity of the composition was stated to be 1.32 g/cm.sup.3. The compositions are not described as being linear viscoelastic and as exemplified do not include any potassium salts.
While the compositions disclosed in U.S. Ser. No. 353,712 provided a satisfactory solution to the problems of phase instability, bottle residue and cup leakage, it has now been found that under some storage and handling conditions and/or processing conditions, additional improvements would be desirable. Specifically, if the viscoelastic composition is subjected to repeated heating and cooling cycles, growth of crystals and product thinning and/or precipitate formation has been observed.
As a result of these problems, the finished product not only may be perceived as unaesthetic but, more importantly, the product viscosity is often lowered which in turn may lead to cup leakage and corresponding degradation in cleaning performance.